An airbag device is provided in a vehicle such as a car. The airbag device has an airbag which is made of a cloth panel and formed into a bag-like shape so that the airbag can be unfolded and inflated to restrain a passenger when unfolding gas is blown into the airbag at the time of collision. In such an airbag device, proper control of the internal pressure of the airbag is required in order to reduce an acceleration peak received by the passenger while inflating the airbag early. To this end, for example, a proposal has been made that the internal pressure is set at relatively high pressure in order to unfold the airbag early immediately after collision, and the pressure is then reduced to reduce the acceleration received by the passenger who has been restrained.
In the background art, it has been general that exhaust units such as vent holes are provided in the airbag and characteristics of the airbag are tuned by the number of the exhaust units, the layout thereof, etc. so that the internal pressure of the airbag can be reduced to proper pressure after the airbag is unfolded and inflated.
In addition, in the background art, a proposal has been made that gas used for unfolding the airbag is cooled to reduce the internal pressure of the airbag to proper pressure.
When a liquid coolant is released at a predetermined timing while or after the airbag is unfolded and inflated, the unfolding gas can be cooled by the heat of evaporation of the coolant to reduce the internal pressure of the airbag. Thus, it is possible to obtain good passenger restraining performance.
As such a coolant releasing device, a device in which a coolant such as an antifreeze solution is sealed in the interior of a cylinder by a piston of silicon rubber etc. and the piston is pressed by use of gas generated by a micro gas generator (MGG) to thereby release the coolant has been proposed, for example, in Patent Literature 1.
In addition, another coolant releasing device in which a coolant is reserved in a tube-like container having a below-like fragile portion formed therein and the container is received in a cylinder so that the container can be compressed axially by a piston to release the coolant has been described in Patent Literature 2.